This invention generally relates to portable light generating devices such as flashlights. More particularly, this invention relates to portable light generating devices that can be manually adjusted to provide in-focus patterns of light that have uniform light intensity throughout the illuminated area and a well defined edge where there is a crisp visual distinction between the illuminated area and the non-illuminated area.
Portable lighting devices, such as flashlights and lanterns, are commercially available in a wide array of embodiments. Some embodiments, particularly lanterns, are designed to produce a broad pattern of light that will illuminate a large area. Other embodiments, such as tubularly shaped flashlights, are intended to produce a narrow pattern of light that brightly illuminates a small area that must be closely inspected. Some flashlights and lanterns include a mechanism that can be used to change the pattern of light from broad to narrow and from narrow to broad as needed and are commonly known as “focusable lights”. Many commercially available focusable lights incorporate an adjustable mechanism that fixes the position of the light bulb within the housing and relies upon movement of the reflector in relation to the light bulb in order to change the diameter of the pattern of light produced by the flashlight. Other focusable lights fix the position of the reflector within the body of the light and then move the light bulb relative to the reflector. Both of these embodiments produce inferior light patterns when adjusted because there is only one optimum location for a bulb relative to the reflector that will produce a pattern of light that is “in focus” thereby producing a well defined and uniform pattern of light at a specified distance from the light. As soon as the relative positioning of the bulb to the reflector is changed, such as when the light bulb is moved and the reflector remains stationary or the reflector is moved and the light bulb remains stationary, the light becomes out of focus and the light pattern becomes distorted. In particular, the perimeter of the light pattern becomes fuzzy or nonexistent. Furthermore, out of focus lights may produce dark spots within the light pattern that result in poor illumination of the object to be inspected.
Therefore, there remains a need for a focusable light that is always in focus thereby enabling the production of well defined patterns of light.